Public health authorities in Belgium are monitoring a localized increase in cutaneous diphtheria cases among the homeless population in the city of Liège. While health officials emphasize that the current situation does not constitute an epidemic, the resurgence of this bacterial infection highlights the persistent challenges of providing healthcare to the most vulnerable members of society.
The Agence wallonne pour une Vie de Qualité (AVIQ), the regional health agency for Wallonia, has identified a cluster of cases specifically affecting individuals living in conditions of extreme precariousness and overcrowding. According to reports from regional news outlets including RTBF, seven cases were recorded in 2025, followed by five additional cases in the most recent period.
As a physician and health journalist, I have seen how “forgotten” diseases often reappear not because of a failure in medical science, but because of gaps in social infrastructure. Diphtheria is a vaccine-preventable disease, and its appearance in a modern European city is a stark indicator of the health disparities facing those without stable housing.
The current outbreak in Liège is characterized by a non-toxigenic strain of the bacteria, meaning the specific samples observed do not produce the dangerous toxin associated with the more severe, systemic forms of the disease. This distinction is critical for the general public to understand, as it significantly lowers the risk of widespread alarm or severe clinical outcomes for the broader population.
Understanding Cutaneous Diphtheria: A Different Manifestation
To understand the current situation in Liège, We see first necessary to distinguish between the two primary forms of diphtheria. Most people are familiar with respiratory diphtheria, which affects the mucous membranes of the nose and throat, often creating a thick gray coating (pseudomembrane) that can obstruct breathing and release toxins into the bloodstream, potentially leading to heart or nerve damage.
Cutaneous diphtheria, however, manifests as skin lesions. It typically presents as a chronic ulcer or a sore that may be covered by a grayish membrane. While it is generally less severe than the respiratory form, it is highly contagious through direct contact with the lesions or contaminated objects. The bacteria responsible, Corynebacterium diphtheriae, find an ideal environment in skin that is broken or irritated, which is more common in individuals lacking access to basic hygiene and wound care.
The prevalence of this form of the disease among the homeless population is often tied to “promiscuité”—the close physical proximity and overcrowding found in emergency shelters or makeshift camps. When people live in cramped conditions without adequate sanitation, a bacterial infection can spread rapidly through a specific social circle, even if the general population remains protected by vaccination.
The Situation in Liège: A Signal of Vulnerability
Lara Kotlar, a spokesperson for AVIQ, has sought to reassure the public by explaining that these fluctuations in cases are not unprecedented among marginalized populations. According to AVIQ, the current rise does not represent an alarmist peak, but rather a fluctuation in a population that has historically been susceptible to such infections.
From a clinical perspective, the fact that the strain is non-toxigenic is the most reassuring detail. In toxigenic diphtheria, the bacteria produce a potent exotoxin that can cause myocarditis (inflammation of the heart muscle) or neuropathy. The non-toxigenic strain primarily causes localized skin infections, which, while requiring medical treatment, do not carry the same risk of systemic failure or death.
However, the appearance of any form of diphtheria serves as a “sentinel event.” In public health, a sentinel event is a signal that something is wrong within a specific demographic. In this case, the cases in Liège point toward a gap in vaccination coverage and a lack of preventative healthcare for the city’s homeless population. Diphtheria is typically prevented via the DTP (Diphtheria, Tetanus, and Pertussis) vaccine, which requires periodic boosters to maintain immunity throughout adulthood.
Public Health Response and Prevention Strategies
In response to the detected cases, the City of Liège is preparing a targeted awareness campaign. This initiative is designed to reach two primary groups: the vulnerable individuals themselves and the field workers—social workers, street medics, and shelter staff—who interact with them daily.
The goals of this intervention are three-fold:
- Early Detection: Training field workers to recognize the signs of cutaneous lesions so that infected individuals can be treated quickly, preventing further spread.
- Vaccination Outreach: Identifying individuals who have missed their booster shots and providing accessible vaccination opportunities.
- Hygiene Support: Improving access to sanitation and wound care to reduce the likelihood of skin breakthroughs that allow the bacteria to enter the body.
AVIQ has emphasized that there is very little risk for the general population. Because the infection spreads primarily through close contact within a specific environment, the likelihood of a person not living in these precarious conditions contracting the bacteria is extremely low. The agency has stressed the importance of avoiding “effets d’annonce”—the panic caused by sensationalized reporting—which can lead to unnecessary anxiety in the community.
Why This Matters for Global Public Health
The events in Liège are a microcosm of a global trend where infectious diseases “cluster” in pockets of poverty. Whether it is the resurgence of tuberculosis or the appearance of cutaneous diphtheria, these outbreaks are rarely about the virulence of the pathogen and almost always about the fragility of the social safety net.
For those of us in the medical community, this serves as a reminder that vaccination programs must be inclusive. A high national vaccination rate can mask dangerous gaps in specific sub-populations. When a segment of the population is “invisible” to the healthcare system, they become a reservoir for diseases that the rest of society believes have been eradicated.
the management of these cases requires a multidisciplinary approach. Medical treatment (antibiotics and wound care) is only half the battle; the other half is social intervention. Without stable housing and hygiene facilities, the risk of reinfection or continued transmission remains high, regardless of the medical intervention provided.
Key Takeaways for the Public
- Low General Risk: The current cases are localized within a specific high-risk group and the strain is non-toxigenic.
- Vaccination is Key: The DTP vaccine remains the most effective defense against all forms of diphtheria.
- Symptom Awareness: Cutaneous diphtheria presents as skin ulcers or sores with a grayish membrane.
- Social Determinants: The outbreak is linked to overcrowding and precarious living conditions, not a failure of the vaccine itself.
The next confirmed checkpoint for this situation will be the rollout of the City of Liège’s awareness campaign and subsequent updates from AVIQ regarding the number of new cases. Health authorities will continue to monitor the strain to ensure it remains non-toxigenic.
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